fragile spiral router bits!!!

[Dick Strauss]

Folks,
I was using a Freud 1/4" spiral router bit for the first time earlier this week. I was trying to cut a circular slot for a pivoting jig. I had a base plate clamped down to the table. The base plate had a hole to accept a 1/4" dowel with a 1" hole around the router bit. The piece to be routed also had a 1/4" hole so that it would pivot on the dowel rod. The first piece went as planned as I plunged through the bottom and cut the slot. I wasn't so lucky with the second one! I had plunged through the 5/16" maple just fine. However, as I began to start routing the rest of the slot, the bit suddenly broke with no verbal warning. I wasn't hurt as the rest of the bit fell harmlessly on the front of the router table.

Was I doing something wrong or are these bits just overly fragile? I've seen the folks on the Router Workshop use these bits for cutting complex patterns with no obvious problems. Has anyone else had this same problem with spiral bits breaking? In the future I don't think I'll be buying or using these bits unless someone can help show me where I went wrong. Any help/thoughts would be appreciated...

Dick

[Carl Eyman]

I've broken 1/8" spiral bits, but not larger. Do you think you were taking too much of a cut?

[Doug Shepard]

Small diameter bits can break easily - spiral or otherwise. I think maybe you're trying to cut too much in one pass (5/16). Years ago I came across some adage that said not to cut more than 1/2 the diameter of the bit depthwise in any one pass. I pretty much try to follow that now. The times I've broken bits have usually been when I've been tried to exceed that amount.

[Dick Strauss]

Guys,
I appreciate what you are saying. I was using very light pressure. I did take the full 1/4" cut but couldn't do it any other way. Imagine you need an arcing slot 1/4" wide in the middle of a board. There is no edge entrance or exit and you need the slot through the full thickness of the board. There is no way to do it without taking at least one full pass with a 1/4" or smaller bit. You can cut a series of holes with a drill press and pivot jig but that will end up with a sloppy slot. That is the way I ended up finishing my slot. Trust me when I say it isn't nearly as neat. I guess I could have removed some material with the drill press first. I might have had better luck if I pre-drilled my entrance hole. I don't know that this would have helped though. If I use a drill press and then use the router it seems like I doing twice the work that I should. Besides, I thought that spiral bits were supposed to be able to drill and route.

Hopefully you have a better idea of what I was doing now. I'm still open to suggestions!

Dick

[Doug Shepard]

Maybe I'm still missing something, but are you saying you couldn't first make a pass cutting 1/8" deep, then make another pass at 1/4" (or 5/16")? If you have the router on a trammel arm to swing through the arc or even with a template and guide collar, you'll end up cutting the exact same path on the 2nd cut, just deeper. I cut the arcing slot on this drill press table that way through 3/4 baltic birch ply and laminate. Each pass removed about 3/16" and I was using a 5/16 or 3/8 bit.
http://www.sawmillcreek.org/showpost.php?p=185091&postcount=3

[pat warner]

Darn right the 1/4" spiral is fragile, most have < an 1/8th of material left in the web after grinding . Cut should be plunge routed in stages. 1/4"/pass in hard wood will often break a 1/4" bit. Straight solid carbide is a stronger bit.
See 621 (http://www.patwarner.com/621_offset.html) for sample of plunger making circles in stages.

[Dick Strauss]

Doug,
I understand what you are saying now. It makes sense. I wasn't ssure if you understood what I was tring to do. I didn't have a start/stop jig set up for these pieces. I was relying on my eyes to tell me where to stop along with some start/stop lines on the boards. Unfortunately you can't see how far you have routed if you are at 1/2 depth on the router table with the board face down like you can on a drill press working the board face up.

It might be that I need to do as you suggest using a start/stop fence set so that I don't have to see what I'm doing.

Thanks,
Dick

[JayStPeter]

I started a thread on spiral bits recently after having the same problem. My 2 spiral bits were from MLCS and Freud. Both broke after < 4" of 1/4"x1/4" fence guided straight cut on my router table. Neither gave any sign of struggle and my feed pressure was not very high.
The recommendation I got was to use Onsrud bits next time and keep the cuts light. I haven't hurried out to get a new spiral bit though.

Jay

[Doug Shepard]

Doug,
I understand what you are saying now. It makes sense. I wasn't ssure if you understood what I was tring to do. I didn't have a start/stop jig set up for these pieces. I was relying on my eyes to tell me where to stop along with some start/stop lines on the boards. Unfortunately you can't see how far you have routed if you are at 1/2 depth on the router table with the board face down like you can on a drill press working the board face up.

It might be that I need to do as you suggest using a start/stop fence set so that I don't have to see what I'm doing.

Thanks,
Dick
Ah - I missed that you were doing it face down on a table. That does complicate things. It's probably easier with the router out of the table on a pivot arm. Then you just go ahead and eyeball the bit to the layout lines, but before you make the first cut. QuikGrip clamp a scrap block to the stock to butt up against the router base at either end of the cut. On the successively deeper cuts I'd also recommend not starting the plunge exactly at the start of the slot but 1/2 to 1" away, then go in the backwards direction to cut to that end. Sometimes the stress of uneven amounts of wood on either side of the bit when you plunge in can cause them to twist and snap.

[Dev Emch]

These type of bits are fragile and often solid carbide which is even more fragile. They do not like lateral pressure. So you need to take proactive steps to reduce this pressure and above all else, take your time! They are great bits when used correctly.

[Ian Barley]

I only use spirals in Cedar these days. I found that 1/2" spirals were breaking taking a 1/4" deep cut in anything else. I still use them in cedar because they give a cleaner finish but for everything else I use two flute straight cutters.

[Mike Vermeil]

For the life of me I still can't figure out what your set-up was, but 1/4" spiral bits are extremely fragile by design. In order to use that bit, you definitely need a set-up that allows multiple shallow passes. Or you might have been able to use a 1/4" straight bit. Maple is hard stuff though, so either way you'd probably need multiple passes.

[George Grubaugh]

I had a 1/8" solid carbide spiral bit roll off of my router table & it broke when it hit the floor.

Yeah, they're fragile!